1. Field of the Invention
The present invention relates to lifting slings and more particularly to lift slings designed for lifting heavy loads such as railroad cars.
2. Description of the Prior Art
Slings for lifting heavy objects such as railroad cars currently comprise a steel saddle or arc adapted to be inserted under a railroad car coupler tongue and a steel rope or cable which passes around the arch with a loop or eye at each end for receiving a hook attached to a crane line or cable. Railroad cars typically weigh between about 30 and 100 tons. A standard sling for lifting each end of the small 30 ton car is made of eight parts of 5/8" inches diameter wire rope and generally weighs about 110 pounds (lbs.). Steel slings for lifting a 60 ton car weigh about 210 lbs.
Two to four men are normally required to lift and position each sling in the confined area under the coupler tongue of the cars. It is not uncommon for workers to sustain injuries to their hands, feet or back in positioning the sling from their sheer mass and weight. Further, wires from the strands of wire rope can, and not infrequently do, break exposing workers to hazardous sharp wire ends which may result in serious hand or arm lacerations.
Slings comprising a core of parallel high tensile strength threads and yarns, such as polyester etc., encased in a protective cover, made of a similar material, are known. See, for example, U.S. Pat. Nos. 3,707,021, 4,232,619, 4,210,089, and 4,850,629. While such synthetic fiber slings are considerably lighter than steel rope, they would not be suitable for lifting objects such as railroad cars. First, the coupler tongue would create highly localized stress points in the sling tending to cut or abrade the covering and core. Second, the ends of the sling which loop around the crane hook would be subject to being cut and/or abraded.
There is a need for a light weight lifting sling which is capable of reliably lifting of heavy objects such as railroad cars.